Summary

The poem Fastitocalon was not, said Tolkien, his own invention entirely but a reduced and rewritten item from old "bestiaries". He found it remarkable that she had perceived the Greekness of the poem through all the corruptions. Tolkien had used a fragment of an Anglo-Saxon bestiary, thinking it was comic and absurd enough to serve as a Hobbit alteration of a more learned Elvish piece, according to his system whereby as English replaces Shire-speech so Latin and Greek replace High-Elven. The original learned name was Aspido-chelöne "turtle with a round shield (of hide)". The corrupted name was astitocalon and a prefixing "F" was added to make the name alliterate.

Tolkien explained that the notion of a treacherous island-monster seems to have come from the East and in Europe it had become mixed up with whales and taken on whale characteristics. In moralizing bestiaries he became an allegory of the Devil, and was so used by Milton.